Ok, How do I know that a provider is not LE.  I'm clear on how to make her comfortable, but what about me?

Tell her that she looks overdressed, and that you want her to relax.  I doubt that female cops would get nude or go topless to make an arrest.

Best you can do is used well reviewd ladies and stay away from streetwalkers and agencies. Always trust your gut. If for some reason you get a bad feeling, get out or don't go. There are plenty of ladies out there but you do not need a hassle.

On male police this would not help at all. Local sheriff dept. has been known to actually have sex with the girls and then bust them. Never heard of it happening with a female cop but who knows. Most likely a female cop would partial strip, probably to her undrwear. Also remember that unless there is video tape involved, it is your word against theirs. The cop is almost always believed.

I found your comment to "stay away from agencies" interesting.  So LE is more likely to work through an agency than pose as an independent?  Is that because LE usually targets agencies, rather than independents, on the provider side and then uses the agencies to get customers?

Mostly a personal prejudice. I live in LA area and some time play in Las Vegas, both areas are known for very bad agencies. However considering that you seldom actually can see the girl in the photo that is the reason you called, when dealing with agencies, they make a great cover for LE. If you stick with independents and turn away any girl who is not the one you saw in the photo, then your chances of getting a ringer are much less.